Method for the adjustment of the spacing between the printing head and the printing media

Abstract: The improvements consist in that the sliding assembly (1) which comprises the movable carriage and the printing head (2) is mounted on a main straight guide (16) parallel to the printing media (6) with simultaneous lengthwise sliding capacity on said main guide as well as pivotation capacity on the same, until the adjustment value of the spacing (4) from the printing head (2) to the printing media (6) is obtained, by the intervention of abutment means to limit the pivotation of said sliding assembly. Said abutment means to limit the pivotation of the sliding assembly (1) are comprised of a second straight guide (11) parallel to the main sliding guide (16) on which second straight guide the sliding assembly is capable of abutting by means of an abutment portion. The sliding assembly (1) comprises two units (7), (8) connected by means of an articulated joint, the mutual position of both units being adjustable as to the angle or rotation, existing means for its locking in the desired position to determine a variable angle position between both units.

Description: This invention refers to improvements in the sliding assembly of plotters and similar apparatus and a method for the adjustment of the spacing between the printing head and the printing media. Usually, in plotters and similar machines a sliding assembly is provided which is capable of sliding along a guide which is parallel to the printing media aimed at receiving the graphic impressions. Said sliding assembly supports the printing head used to carry out the printing on the corresponding media usually by means of the projection of jets of ink, ink bubbles or other methods. One of the problems affecting the performance of plotters and other apparatus of similar type consists in maintaining a controlled spacing between the outlets of the nozzles used for the projection of the jets of ink in the printing heads and the printing media aimed to receive such projections. When said spacing between the outlets of the nozzles and the printing media is smaller than a predetermined spacing or exceeds the same, the printing is liable to show faults. In case of a too big spacing, the ink jet will be too wide at the moment of impinging on the printing media and the printed marks will be too big and the edges fuzzy. When the spacing is too small the ink will not spread properly on the printing media, its drying will be slower and smearing is liable to occur. The way to usually attack such problems consists in determining tight tolerances for the parts forming the sliding assembly as well as its corresponding guiding and driving means, in order that the positioning of the printing head respect of the printing media to receive the ink markings meet the predetermined value of said spacing with a more acceptable tolerance. However, this process requires the machining of the parts of the sliding assembly with very close tolerances which means a high cost of manufacture while the solution given to the above problem is less than satisfactory as the addition of tolerances does not easily allow to maintain a well controlled spacing between the outlets of the ink nozzles and the printing media which will receive the ink projections. Some attempts have been made in this field to try to adjust the spacing between the printing head and the printing media. U.S. Patent nº 5087141 to Kieran B. Kelly issued on February 11, 1992 discloses a system comprising an intermediate bar or roller contacting the printing paper, performing a pinching action on the drive roller while the carriage bearing the printing head and the intermediate bar has a pivoting movement being capable by this arrangement to refer the position of the printing head to the printing media, regardless of the thickness of this latter. The system is aimed at permitting the apparatus to operate with different thicknesses of printing media, but it is not aimed nor has the means to adjust the actual value of the spacing between the printing head and the printing media, as in the present invention. Document EP-A-0 479 270 to Canon refers to a recording apparatus which comprises a recording head and means for changing the distance between the recording head and the recording medium by changing the height of the carriage, the height being measured from a supporting member. To find a solution to the above problem which is common to the ink jet printing systems known heretofore, this invention has as an objective to provide new means and the corresponding method for the adjustment of the spacing between the outlets of the ink nozzles and the printing media which has to receive the ink projections, whereby said spacing may be kept within the desired tolerance range substantially regardless of the tolerances of the individual parts, which may be manufactured at a lower cost. Another objective of this invention consists in permitting to keep a narrower tolerance range for the spacing between the outlet of the ink nozzles and printing media. Another additional objective of this invention consists in providing means and a method for the determination and adjustment of the spacing between the outlets of the ink nozzles and the printing media requiring a lower number of parts than usual in the prior art. Another objective of the present invention consists in that once the adjustment of the spacing between the outlets of the nozzles for the ink and the printing media has been made, said spacing has a remarkable stability during the service life of the apparatus. Another objective consists in providing the means in order that the adjustment of the spacing between the printing head and the printing media may be carried out easily and in a short time. To achieve these objectives, the present invention provides a sliding assembly, which comprises the movable carriage and the printing head with the nozzles for the injection of the ink, constituted by two interconnected units, so that the following conditions are met: a) the sliding assembly engages the main guide which determines the path of the printing head, having capacity not only for lengthwise sliding but also for pivotation on said main guide until the desired adjustment position for the printing head in relation to the printing media is obtained, the extent of said pivotation being determined by abutment means limiting the pivotation of said sliding assembly; b) the abutment means which limit the pivotation of the sliding assembly comprise a second straight guide parallel to the main guide, said second straight guide being contacted by an abutment portion of the sliding assembly; c) the two units forming the sliding assembly are interconnected to each other by means of an articulation joint adjustable in rotation and capable of being blocked in a position which determines a variable pivotation position between both units of said sliding assembly; d) one of the units of the sliding assembly is guided on the main sliding guide while the second unit engages the second straight guide by means of an abutment portion; e) the sliding assembly has means for the variation of the pivotation position of both units of the sliding assembly on its articulation joint, which means may be rigidly blocked in the desired position; f) the center of gravity of the sliding assembly is offset with respect to the main guide, lying on the side of the assembly corresponding to the printing head, whereby the printing head has a tendency to swivel towards the printing media; and g) both the main straight guide as well as the second abutment guide are machined on the same one piece support frame. By this arrangement, the invention permits the sliding of the assembly guided both by the main straight guide and the second abutment guide which limits the pivotation of the assembly. The pivotation of the assembly is stable during the operation of the machine because of the offset arrangement of the gravity center as explained under e). This effect may be enhanced by eventual pre-loading springs. At the same time, it is possible to adjust the correct spacing between the outlets of the ink nozzles and the printing media in a adjustment step to be carried out after the final assembly of the plotter, on which occasion the relative rotation of both units forming the sliding assembly on the shaft of its articulated joint is provoked until the precise height or spacing between the outlets of the injection nozzle and the printing media is obtained. Then, the relative position between both units will be rigidly blocked to permit that said correct spacing be maintained so that the separation between the outlets of the injection nozzles and the printing media will be equally maintained substantially regardless of the tolerances of manufacture of the individual parts. At the same time, given the rigid blocking of the relative position between both units forming the sliding assembly, said spacing will be practically maintained constant along the service life of the machine or alternatively until a new value is chosen for said height or adjustment of the printing head to the printing media, which new adjustment may be carried out in a simple and fast way unblocking, adjusting and blocking again the articulated joint. Alternatively, the blocking effect may be obtained by the self-screwing action of the adjustment screw. Therefore, the adjustment method which forms part of the present invention will be characterized in that in an arrangement as provided by the present invention the following operation steps will be carried out: i) Measurement of the actual spacing between the outlets of the ink nozzles and the printing media by means of any suitable type of measurement device; ii) To proceed to the relative rotation of both units forming the sliding assembly on the rotation shaft of the articulated joint until the predetermined spacing between the outlets of the ink nozzles and the printing media is obtained; and iii) Locking both units of the sliding assembly to each other, cancelling the capacity for relative rotation to one another on the shaft of the articulated joint. The step i) may be carried out by any suitable measurement means for example by external fixed gauges, for instance balls, or by means of measuring devices with optic distance detection means or other contactless distance detecting means to be attached to a portion associated to the printing head in order to accurately gauge said spacing. The measuring means will be preferably associated to optical display means to show the actual value of the spacing. Said measurement operation will eventually comprise the accurate determination of the spacing in different positions of the sliding assembly along the main guide, with the aim to evaluate the eventual differences along the path of the sliding assembly allowing whenever desired the averaging of said measurements. The relative rotation of the two units forming the sliding assembly and its locking together after the adjustment of the spacing will be carried out by any suitable means without essentially affecting this invention. Preferably, said relative rotation will be carried out by a simple system comprising a screw and fixed nut together with a bias spring. The rigid locking of the parts may be carried out by means of adhesive or a solidifiable mass, for instance a wax or resin material whereby after its solidification the constant position between both units may be easily maintained. For its better understanding, a non limiting preferred embodiment of the invention will be explained in the following with reference to the attached drawings, in which: Figure 1 shows schematically a cross section of the sliding assembly carrying the printing head of a plotter, according to the present invention. Figure 2 shows a view similar to figure 1 along a parallel section plane. Figure 3 shows a detail in cross section of the articulation of the two units forming the sliding assembly. Figure 4 shows a perspective view of the sliding assembly of figures 1 and 2. This invention refers to the means to allow the movement of the sliding assembly -1- of a plotter or similar apparatus, comprising the printing means or printing head schematically shown with reference numeral -2-, said printing means being aimed at carrying out the graphic marks on the printing media guided by a drum or similar part -3- of the apparatus. For a better understanding the drawing does not show the media to receive the printing nor the driving and guidance means for the same which are conventional in this field of the technique. The main objective of the present invention consists in permitting an easy adjustment of the spacing between the printing media and the printing head, that is, between the outlets of the injection nozzles and the printing media, permitting at the same time that said spacing may be maintained during the operation of the apparatus. Said spacing has been indicated with the reference numeral -4-, consisting in the spacing between the dot and dash lines -5- and -6- which, respectively, represent the lower edge of the ink injection nozzles and the media to receive the graphic marks. The present invention provides that the sliding assembly -1- which has been represented perpendicular to the plane of the drawing, in order to carry out the printing on the printing media on the drum -3- at a level shown by the dot and dash line -6-, comprises two units -7- and -8- interconnected by means of an articulated joint with a rotating shaft shown by reference numeral -9-, the improvements providing means to permit the variation of the rotation position between units -7- and -8- by means of pivotation on the shaft -9-, said means being represented as an example in figure 3 by an adjustable screw -10-, which will be explained in more detail in the following. The sliding assembly -1- comprising the two units -7- and -8- is movable on a path which is parallel to the printing support by engaging the main straight guide -19- along which it may slide by the operation of driving means which have not been represented, with capacity to pivotate on said main guide. To limit the pivotation of the sliding assembly on the main guide, a second guide -11- is provided parallel to said main guide -19- on which second guide a portion of the body -7- abuts when the sliding assembly pivotates on the main guide, limiting in this way the angle of rotation of said assembly -1-. As it will be easily understood, the pivotation of the assembly -1- will determine the spacing or height -4-of the printing head to the printing media -6-, so that it will be easy to make the adjustment of said spacing -4- in a final step of the assembly of the apparatus substantially regardless of the individual tolerances for the manufacture of the parts as it will be sufficient to make the adjustment of the two units -7-, -8- to each other on the rotation shaft -9- in order that the pivotation angle of the assembly -1- may be accurately adjusted to have a predetermined spacing -4-. To make the relative rotation between units -7- and -8- of the sliding assembly -1- easier, the invention provides, as an example, an adjustment mechanism comprising an screw -10- which, as shown in figure 2, is under bias of an spring -12-, engaging at the same time a fixed nut -13- or similar fixed threaded portion. In this way, by turning the screw -10- clockwise or counter-clockwise, collaborating with the action of spring -12-, it will be possible to adjust the relative positions of units -7- and -8- which constitute the sliding assembly -1-. After having obtained the predetermined relative position of rotation of the units -7- and -8- which will determine in its turn the desired spacing -4-, the further rotation of the screw -10- will be prevented, if desired, by any suitable positive means, avoiding that said spacing -4- may be unintentionally disadjusted during the operation of the apparatus. Among the methods which may be used for said locking action, the use of a fluid solidifiable mass to be poured within the cavity -14- for the head of the screw -10- or between the screw and its nut may be contemplated, for instance, a wax or resin which after solidification will prevent any unintentioned rotation of the screw -10-. As will be easily understood in case of wishing to change the spacing -4- according to eventual changes in the set up of the apparatus, it will be sufficient to eliminate the locking means and reproduce the above mentioned adjustment process. The blocking of the screw -10- may be obtained as well by the self-screwing effect of the tip of said screw on the unit -8-, for instance, the wall -20-. According to the present invention, the main guide will preferably comprise a circular cross section precision machined bar -19-, resting on a wall -16- of the body -17- of the apparatus, preferably obtained by light alloy extrusion, said body comprising as well the secondary guide -11-. Any other type of suitable straight guide could be used provided that it permits the guidance of the assembly -1- perfectly parallel to the printing media -6- and that at the same time it permits the pivotation of said assembly -1- around an horizontal center line to permit the adjustment of the above mentioned printing spacing. Likewise, the guide -11- will comprise preferably a flat straight guide as shown in the figures, preferably machined together with the wall -16- or the support for this latter to obtain a satisfactory parallelism. Said guide will be engaged by one or more rollers -15- mounted on a portion of the unit -7-. These rollers might be substituted by friction bushings or similar. The sliding assembly -1- may be incorporated on the main guide -19- according to any suitable arrangement permitting its displacement along the guide and its simultaneous pivotation on the same. In figure 2, an embodiment has been shown with partly encircling bushings -18- or a similar arrangement in the lower part of the sliding assembly to permit the arrangement of the assembly -1- centered and guided on the bar -19-, permiting its rotation without interfering with the upper rims of supporting wall -16-. To improve the stability of the sliding assembly -1- in relation with the main guide, these improvements provide that the center of gravity of the assembly be offset in relation to said main guide, displaced towards the printing head, that is, opposed to the second abutment guide -11-, whereby the assembly -1- will have the tendency by its own weight to adopt a stable position corresponding to the pivotation arrangement chosen to make the spacing -4- to correspond with the desired value. To further improve the stability of the sliding assembly -1-, abutting against guide -11-, pre-loading springs could be eventually incorporated to exert a certain pressure on said guide -11-. As will be easily understood, an apparatus incorporating the improvements of this invention, having the means which have been explained in the aforegoing, will entail a process for the adjustment of the spacing of height of the printing unit characterized by the following steps: i) measurement of the actual spacing -4- between the outlet of the ink nozzles and the drum -3- to support the printing media, by means of any suitable type of measurement device; ii) to proceed to the relative rotation of both units -7- and -8- forming the sliding assembly -1- on the rotation shaft -9- of its articulated joint up to obtaining the predetermined spacing -4- between the outlets of the ink nozzles and the printing media; and iii) optionally proceeding to rigidly locking both units -7- and -8- of the sliding assembly -1- cancelling the capacity for relative rotation to one another on the shaft -9- of the articulated joint. The step i) may be carried out by means of external fixed gauges for instance by means of balls or incorporating a sensing pen in the printing head, capable to directly indicate the actual value of the spacing or height -4-, by means of a dial or a visual display. The step ii) will be carried out according to one prefered embodiment of this invention, in the form which has been shown in the figures, by simple rotation in the desired sense of the screw -10- which operates together with the fixed nut or similar threaded portion -13- and the spring -12-. If desired, the step iii) will be carried out, for instance, by means of the introduction of a solidifiable mass in the cavity -14- receiving the head of the screw -10- or by self screwing of this latter or by any other suitable means. This invention has been explained according to a preferred embodiment of the same, as shown by the enclosed drawings. However, it will be understood that the details of said embodiment are not limitative for the invention and that any expert in the art will be able to introduce many variations in the invention which will be included within the scope of the enclosed claims.

Claims: A sliding assembly for a plotter or similar apparatus having means for adjustment (10) of the spacing (4) between printing head (2), supported by the sliding assembly, and a printing media (6); the sliding assembly comprising a movable carriage mounted on a main straight guide (16) parallel to the printing media (6) so as to have simultaneously sliding and pivotation capacity on the said guide (16), wherein the pivotation is limited by the intervention of abutment means so as to set the spacing (4) and the sliding assembly comprises two units connected by means of an articulated joint (9) so that the spacing (4) is adjustable by the relative rotation of the two units (7, 8) about the articulated joint (9) and wherein said means for adjustment (10) are capable of adjusting the spacing (4) among a substantially continuous sequence of values comprised between a first and a second predetermined adjustment values. A sliding assembly as claimed in claim 1, wherein said abutment means comprise rotating abutment means (15). A sliding assembly as claimed in claim 1, further comprising locking means for locking the two units (7) (8) of the sliding assembly so as to substantially prevent relative rotation between said units. A sliding assembly as claimed in claim 1, wherein the printing head (2) and abutment means are located on substantially opposite sides of the main straight guide (16). A sliding assembly, according to claim 1, characterized in that the abutment means to limit the pivotation of the sliding assembly (1) are comprised of a second straight guide (11) parallel to the main sliding guide (16) on which second straight guide the sliding assembly is capable of abutting by means of an abutment portion. A sliding assembly, according to the previous claims, characterized in that one of the units (8) of the sliding assembly is guided on the main sliding guide, while the other unit (7) abuts on the second straight guide by means of an abutment portion. A sliding assembly, according to the previous claims, characterized in that the abutment portion of the sliding assembly (1) which collaborates with the second straight guide (11) is comprised of rollers (15) mounted on a portion of the sliding assembly (1). A sliding assembly, according to the previous claims, characterized in that the abutment portion of the sliding assembly (1) which collaborates with the second straight guide (11) is comprised of friction bushings mounted on a portion of the sliding assembly (1). A sliding assembly, according to the previous claims, characterized in that the center of gravity of the sliding assembly (1) is offset in respect of the main sliding guide, towards the side which corresponds to the printing head (2). A sliding assembly, according to the previous claims, characterized in that the main guide for the sliding assembly (1) is constituted by a precision circular cross section bar (19) resting on a supporting wall (16) of the body of the apparatus. A sliding assembly, according to the previous claims, characterized in that both the supporting wall (16) of the body of the apparatus for receiving the cross section bar (19) as well as the second abutment guide (11) are machined on the same one-piece supporting frame (17) of the plotter. A sliding assembly, according to the previous claims, characterized in that the means to adjust the relative rotation of both units (7), (8) of the sliding assembly (1) is constituted by an adjustment screw (10) which supports the action of a bias spring (12) and which is capable to engage a fixed nut or similar fixed threaded portion (13). Method for the adjustment of the spacing between the printing head and the printing media of a plotter or similar machine, comprising the sliding assembly of claims 1 to 12 characterized in the following operative steps: i) measurement of the actual spacing (4) between the outlets (5) of the ink nozzles and the drum supporting the printing media (6) by means of any suitable type of measurement device; ii) selecting a desired adjustment value of the spacing (4) between the printing head and the printing media, among a substantially continuous interval of values comprised between a first and a second predetermined adjustment values, said step (ii) of selecting further comprises the step of proceeding to the relative rotation of both units (7, 8) of the sliding assembly (1) on the rotation shaft (9) of its articulated joint until the desired adjustment value of the spacing (4) is obtained. iii) locking both units (7), (8) of the sliding assembly cancelling the capacity for relative rotation to one another on the shaft (9) of the articulated joint. Method of adjustment, according to claim 3 characterized in that, the measurement of the actual value of the spacing (4) between the outlets of the ink injection nozzles (5) of the printing head (2) and the drum (3) to support the printing media (6) is carried out by means of fixed gauges or by a distance sensor incorporated into the printind head (2), associated to a dial or visual display for the indication of the value of said spacing. Method of adjustment, according to claim 13 characterized in that, the locking in position of the articulated joint after the adjustment of the pivotation is carried out by means of a fluid solidifiable mass to be poured into housing (14) for the head of the adjustment screw (10), or between the screw and its nut. Method of adjustment, according to claim 13 characterized in that, the locking in position of the articulated joint after the adjustment of the pivotation is carried out by means of self screwing of adjustment screw (10) on a portion of the sliding assembly (1).

Inventors: GARVI JOAQUIN BRUGUE, GARVI, JOAQUIN BRUGUE, Garvi, Joaquin Brugué
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1994
Main classification: B41J25
IPC codes: B41J25